This Application is directed, in general, to fault current protection and, more specifically, to fault detection with a use of an array of magnetic sensor, such as an integrated magnetic sensors.
Residential mains installations are required by regulations to be equipped with residual (fault) current detectors. These detectors detect the presence of a leakage path (insulation fault or human body) by assessing the difference of live and neutral wire currents. When that difference exceeds a threshold, e.g. 30 mA, a relay is opened to protect the installation or human touching a live conductor. It is also anticipated that white goods will be required to be equipped with such protection, also for emerging markets, where the earthing rules may not be always observed. Generally, protection may need to be integrated in the mains plug, to also detect faults in the mains cable itself.
Generally, the prior art produces a difference in a magnetic domain, by passing live and return (neutral) currents through wires wound on the same magnetic core. In case of a fault, the difference in magnetic flux will pass a 3rd coil and drive a normally-closed relay directly or will be detected by a magnetic sensor, e.g. a Hall sensor, to drive a relay.
Generally, when a leakage current occurs, this will affect the magnetic field around the current carrying conductor. This magnetic field can be compared with, for example, an ‘ideal’ magnetic field, or with a magnetic field of a second conductor. This can be done with an flux sensor (IFG), such as discussed “A Digital Fluxgate Magnetic Sensor Using Sigma-Delta Modulation for Weak Magnetic Field Measurement” by S. Kawahito, et al, EEEE International Instruments and Measurements Technology Conference, pages 257-260, May 2002.
FIG. 1A illustrates a prior art approach of measuring a magnetic field with an Flux Gate sensor. In FIG. 1A, the sum of the field around the two conductors is zero when perfectly matched. Therefore, this field around the conductors needs a concentrator to measure any slight but nonetheless important variation. The field between the conductors is large, double that of each individual conductor.
FIG. 1B illustrates a prior art fluxgate sensor and concentrator. As is illustrated, the current is flowing in opposite directions, which requires a concentrator 110 to concentrate the magnetic field of the two conductors 120, 125. A magnetic field sensor can be placed in the slot of the concentrator 110 for sensing the fault current.
FIG. 1C illustrates a prior art current sensor module, the magnetic field sensor is a Fluxgate sensor in a circular ring form. The flux gate sensor is surrounded by 2 magnetic shields or concentrators for isolation and field concentration or common mode field reduction.
Therefore, there is a need in the art as understood by the present inventors for improved approach to sensing fault currents.